Curious System Solutions, LLC

Bringing dreams to life

Here at Curious System Solutions, LLC our human/man machine interface (HMI/MMI) work focuses on embedded devices.  Our preference is for interfaces that have as few moving parts as possible, preferably none.  We use capacitive sensors to create interfaces with buttons, dials and sliders.  They can work with gloves and liquid on the buttons.  Many popular portable personal music devices use this style of interface.  Feedback and status are acomplished using LEDs, LCDs and audio.  With these components, we can create a low cost interface that has no movable parts and can be environmentally protected.  All these qualities make this an ideal interface for industrial environments where a piece of equipment may last 20 years, or has lasted 20 years and needs an update.

With all that said, we are fans of a nice solid knob and a big red button.  We know what we can do to keep your product robust and stylish.  We help you find the right interface for your device.  We realize how important an intuitive interface is in both the efficiency and marketability of a product.

Design Questions

The first things to do when designing or redesigning an interface is to look at where, when, how and whom will use it.

How will it be used?

This question brings together the rest of the questions.  This is the first and last question that we ask.  It is first because it helps us picture the device and everything around and interacting with it.  We ask it last to make sure that our original idea of how it will be used is still valid after asking the other questions and looking at details.  If our ideas of how it will be used have changed from the beginning of the exercise to the end, we need to ask the other questions again to make sure our answers there are valid.

Where will it be used?

When looking at where an interface will be used, we need to consider all the elements that affect a person or equipment in the environment.  Take a minute to consider each one.

  • Temperature - Are the interface components going to be subjected to extreme hot or cold?  Material and component choices may require operation over an extended temperature range.
  • Humidity - Will the device have to be sealed to prevent humidity from ruining it?
  • Hazardous materials - Will the device have to be sealed to prevent liquid, gas or solid particulates from entering it and destroying it.  Will the exterior materials have to be acid resistant?  Are their other solvents that are a concern?
  • Lighting - Will lighting be uniform where the device is used?  Will the lighting change over time?  If it does, an ambient light sensor can be included to change the relative intensity of the interface lighting.
  • Airborne particulate - This, like hazardous materials, is a concern for contamination and corrosion of the interface.
  • Space constraints - How much room do I have for the interface.  This determines the total space to trade between different interface elements.
  • Physical abuse - Will the interface be dropped?  Is it possible that it may have point impacts?  Thinking about possible physical trauma will help decide the physical materials and design of the interface.
  • Power limitations - How much power can the interface use?  Is it attached to mains or does it use a battery source?  If it is power limited, the use of LEDs and audio may need to be curtailed.

When will it be used?

When a device is used has an impact on the environment and the user.  Three considerations here are:

  • Day/Night operation - Does the device have to work in low/no light conditions, bright direct light, or both?  This will impact the choice of displays and labeling for buttons and sliders.
  • User mental state - Will the user be waking from a deep sleep or have to use the interface for a long period of time?  If a user is coming out of a deep sleep, the interface must be simple and transmit information slowly enough that it is not missed by the user.  If the interface is used over a long period of time by a person, important elements of the interface need to stick out.  Do not make a critical indication the difference between two closely spaced lights or the difference between a bright light and a brighter light.
  • Frequency of operation - Is the interface used continuously or can it have a "sleep" mode to conserve energy.  If someone only uses it infrequently, the device status needs to be quickly discernible, especially if it is for critical or life threatening equipment.

Whom will use it?

Understanding the user is critical in the design of a human machine interface.  Some considerations are:

  • Familiarity and training - Interfaces that require little familiarity or training often require more space to separate the controls and lead the operator through the proper way to operate the device.  Other options are audio prompts or a built-in help system.  If there is little training of the operator, the device often needs to protect the user from himself by prompting the user for a confirmation after explaining possible side effects of the action.  Another way of doing this is by implementing hardware or software interlocks in the interface.
  • Attentiveness - If there are many things going on with the user, the interface design needs to provide sufficient notice to the user so that they will not miss critical items of information.
  • Color blindness - There are several types of color blindness in the general population red/green and blue/yellow color blindness.  Take this into account when designing the interface.  Do not assume that the operator can tell the difference between the same light blinking red or green.
  • Clothing - Does the work environment require the user to wear heavy gloves?  If it does, the interface will need controls that are spaced farther apart than would be for bare hands.
  • Hearing impairments - Audio prompts may not work if the user is hearing impaired or the environment is too noisy to hear effectively.
  • Blindness - If your interface has to be accessible to those who are visually impaired, labeling of controls should include physical ridges to show where the different controls are along with braille test telling what they do.  There are three options for feedback: heat, audio and tactile.  Controls can be designed so that resting a finger on them does not change them, but has an audio prompt of their state.  Different controls can also have a resistive heater put under them so that a relative temperature can be sensed.  Tactile feed back is the hardest of the three for capacitive touch sensors, since they don't have any moving parts.  This is an area where research is currently being done.

Design Capture

Write your answer down to these question.  Now give it to someone else and have them describe back to you, in their own words.  Do this for each question.  If their description is different from yours, it is probably because you a) left out some details, or b) were not specific enough in your description to rule out other possible methods of use.  Rewrite it until the usage is clear.  This is important because it provides something permanent (your memory is not permanent) that you can reference through out the design process.  If you are not the designer, it provides a good overview of what the device is so that your design engineer(s) are building the same thing you are.

Writing down the answers to these questions also helps provide protection against design creep.  How many of you have had a boss or customer who "remembers" that something was included in the original design?  Having a document to reference back to helps you to keep your design target from moving on you, which is a good thing.

If you would like to learn more about decisions for a HMI/MMI and have us help you in reviewing or designing your, please contact us.


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